Characteristics of the circular subsonic laminar jets flow with an initial Poiseuille profile

Abstract In this work, the experimental data are compared with the version of the “strong” jet (Re ≫ 1) of the exact Landau-Squire solution. The experiments were performed for a submerged air jet flowing out of a tube with a diameter of D = 3.2 mm and a length of more than 100D at a Reynolds number equal to Re = 436. The initial conditions in the jet are the Poiseuille velocity profile, the level of velocity pulsations is less than 1%. Measurements were carried out using a hot-wire anemometer. It is shown that satisfactory agreement with theory is achieved at distances from the tube starting from x/D = 5.6 and up to the zone of transition to turbulence (x/D > 35). Turbulence along the jet axis will increase from 1% to 2.5%, while in the mixing layers it increases to 4.7%.

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Separation in oscillating laminar boundary-layer flows

Journal of Fluid Mechanics ◽

10.1017/s0022112071000909 ◽

1971 ◽

Vol 47 (1) ◽

pp. 21-31 ◽

Cited By ~ 52

Author(s):

R. A. Despard ◽

J. A. Miller

Keyword(s):

Experimental Data ◽

Boundary Layer ◽

Experimental Investigation ◽

Reynolds Number ◽

Reverse Flow ◽

Oscillation Amplitude ◽

Hot Wire ◽

Boundary Layer Flows ◽

Laminar Boundary Layers ◽

History Of

The results of an experimental investigation of separation in oscillating laminar boundary layers is reported. Instantaneous velocity profiles obtained with multiple hot-wire anemometer arrays reveal that the onset of wake formation is preceded by the initial vanishing of shear at the wall, or reverse flow, throughout the entire cycle of oscillation. Correlation of the experimental data indicates that the frequency, Reynolds number and dynamic history of the boundary layer are the dominant parameters and oscillation amplitude has a negligible effect on separation-point displacement.

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Control of a Round Jet Intermittency and Transition to Turbulence by Means of an Annular Synthetic Jet

Actuators ◽

10.3390/act10080185 ◽

2021 ◽

Vol 10 (8) ◽

pp. 185

Author(s):

Zuzana Antošová ◽

Zdeněk Trávníček

Keyword(s):

Reynolds Number ◽

Active Control ◽

Flow Regimes ◽

Velocity Profiles ◽

Synthetic Jet ◽

Transition To Turbulence ◽

Jet Flows ◽

Maximal Effect ◽

Hot Wire ◽

Round Jet

This paper deals with active control of a continuous jet issuing from a long pipe nozzle by means of a concentrically placed annular synthetic jet. The experiments in air cover regimes of laminar, transitional, and turbulent main jet flows (Reynolds number ranges 1082–5181). The velocity profiles (time-mean and fluctuation components) of unforced and forced jets were measured using hot-wire anemometry. Six flow regimes are distinguished, and their parameter map is proposed. The possibility of turbulence reduction by forcing in transitional jets is demonstrated, and the maximal effect is revealed at Re = 2555, where the ratio of the turbulence intensities of the forced and unforced jets is decreased up to 0.45.

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Jet-to-Plate Distance Effect on Heat Transfer From a Flat Plate to an Impinging Jet at Various Reynolds Numbers

Volume 7: Fluids and Heat Transfer, Parts A, B, C, and D ◽

10.1115/imece2012-87746 ◽

2012 ◽

Author(s):

Patricia Streufert ◽

Terry X. Yan ◽

Mahdi G. Baygloo

Keyword(s):

Heat Transfer ◽

Experimental Data ◽

Reynolds Number ◽

Flat Plate ◽

Numerical Solutions ◽

Stokes Equations ◽

Local Heat Transfer ◽

Reynolds Numbers ◽

Air Jet ◽

Plate Distance

Local turbulent convective heat transfer from a flat plate to a circular impinging air jet is numerically investigated. The jet-to-plate distance (L/D) effect on local heat transfer is the main focus of this study. The eddy viscosity V2F turbulence model is used with a nonuniform structured mesh. Reynolds-Averaged Navier-Stokes equations (RANS) and the energy equation are solved for axisymmetric, three-dimensional flow. The numerical solutions obtained are compared with published experimental data. Four jet-to-plate distances, (L/D = 2, 4, 6 and 10) and seven Reynolds numbers (Re = 7,000, 15,000, 23,000, 50,000, 70,000, 100,000 and 120,000) were parametrically studied. Local and average heat transfer results are analyzed and correlated with Reynolds number and the jet-to-plate distance. Results show that the numerical solutions matched experimental data best at low jet-to-plate distances and lower Reynolds numbers, decreasing in ability to accurately predict the heat transfer as jet-to-plate distance and Reynolds number was increased.

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Investigation of the Effect of Inlet Turbulence on Transitional Wall-Bounded Flows

Volume 1B, Symposia: Fluid Measurement and Instrumentation; Fluid Dynamics of Wind Energy; Renewable and Sustainable Energy Conversion; Energy and Process Engineering; Microfluidics and Nanofluidics; Development and Applications in Computational Fluid Dynamics; DNS/LES and Hybrid RANS/LES Methods ◽

10.1115/fedsm2017-69321 ◽

2017 ◽

Cited By ~ 1

Author(s):

Burak Ahmet Tuna ◽

Xianguo Li ◽

Serhiy Yarusevych

Keyword(s):

Boundary Layer ◽

Turbulence Intensity ◽

Initial Conditions ◽

Hydraulic Diameter ◽

Transition To Turbulence ◽

Duct Flow ◽

Entrance Length ◽

Hot Wire ◽

Boundary Layer Development ◽

Layer Development

The present work investigates experimentally the effects of grid-generated turbulence on the transition and the hydrodynamic entrance length in a developing duct flow. Particle Image Velocimetry (PIV) and hot-wire anemometry are used to characterize the flow in a rectangular duct with a length of 1m (∼40Dh) and an aspect ratio of 2 (20mm × 40mm). The inlet turbulence intensity is controlled using different grids, and experiments are performed for a Reynolds number based on hydraulic diameter ReDh = 17,750. Hot-wire and PIV results show that the inlet turbulence intensity has a substantial effect on the flow evolution in the duct, as it substantially changes the boundary layer characteristics in the hydrodynamic entrance region. Analysis shows that, as expected, transition to turbulence advances upstream as the inlet turbulence intensity increases, leading to the decrease in the entrance length. The primary effect is confined to boundary layer development, as the turbulence intensity decays rapidly in the core flow, becoming independent of the initial conditions after about 10 hydraulic diameter (Dh) downstream from the grid. Thus, the analysis is focused on characterizing the boundary layer development and quantifying the associated changes in the flow development along the duct.

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Dynamics of spatially localized states in transitional plane Couette flow

Journal of Fluid Mechanics ◽

10.1017/jfm.2019.154 ◽

2019 ◽

Vol 867 ◽

pp. 414-437 ◽

Cited By ~ 4

Author(s):

Anton Pershin ◽

Cédric Beaume ◽

Steven M. Tobias

Keyword(s):

Reynolds Number ◽

Couette Flow ◽

Initial Conditions ◽

Reynolds Numbers ◽

Localized States ◽

Transition To Turbulence ◽

Dynamical Structure ◽

Plane Couette Flow ◽

Homoclinic Snaking ◽

Chaotic Transients

Unsteady spatially localized states such as puffs, slugs or spots play an important role in transition to turbulence. In plane Couette flow, steady versions of these states are found on two intertwined solution branches describing homoclinic snaking (Schneider et al., Phys. Rev. Lett., vol. 104, 2010, 104501). These branches can be used to generate a number of spatially localized initial conditions whose transition can be investigated. From the low Reynolds numbers where homoclinic snaking is first observed ($Re<175$) to transitional ones ($Re\approx 325$), these spatially localized states traverse various regimes where their relaminarization time and dynamics are affected by the dynamical structure of phase space. These regimes are reported and characterized in this paper for a $4\unicode[STIX]{x03C0}$-periodic domain in the streamwise direction as a function of the two remaining variables: the Reynolds number and the width of the localized pattern. Close to the snaking, localized states are attracted by spatially localized periodic orbits before relaminarizing. At larger values of the Reynolds number, the flow enters a chaotic transient of variable duration before relaminarizing. Very long chaotic transients ($t>10^{4}$) can be observed without difficulty for relatively low values of the Reynolds number ($Re\approx 250$).

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Effects of Cylinder Diameters, Reynolds Number and Distance Between Two-Tandem Cylinders on the Wake Profile and Turbulence Intensity

ASME-JSME-KSME 2011 Joint Fluids Engineering Conference: Volume 1, Symposia – Parts A, B, C, and D ◽

10.1115/ajk2011-15020 ◽

2011 ◽

Author(s):

Amin Rahimzadeh ◽

Majid Malek Jafarian ◽

Amir Khoshnevis

Keyword(s):

Reynolds Number ◽

Velocity Profile ◽

Turbulence Intensity ◽

Stream Velocity ◽

Hot Wire ◽

Velocity Defect ◽

One Dimensional ◽

Tandem Cylinders ◽

Cylinder Diameter ◽

Spacing Ratio

A series of experimental and numerical investigations on two tandem cylinders wake have been studied. The velocity profile and turbulence intensity have been acquired by a single one dimensional Hot Wire anemometer. The two cylinders were mounted in a tandem manner in the horizontal mid plane of the working section. The effect of the upstream cylinder diameter, Reynolds number and the distance between the cylinders on the wake profile and turbulence intensity on the downstream cylinder was investigated, while the Reynolds number ranged between 1.5× ⟦10⟧ ^4 ∼ 3× ⟦10⟧ ^4. The upstream cylinder diameter (d) was 10, 20 and 25 mm, while the downstream cylinder diameter (D) was 25 mm, corresponding to d/D ranging from 0.4 ∼1.0. The spacing ratio L/d (where L is the distance between the upstream cylinder center and the leading stagnation point of the downstream cylinder) was 2 and 5.5, covering different flow regimes. Observations indicate that two symmetric turbulence intensity peak will occur at mean velocity gradient area. Turbulence area will increase in width for both L/d = 2 and 5.5 as increasing distance from the cylinder (x/D) and decreasing free stream velocity. But totally the range of the turbulence area for L/d = 5.5 is greater than L/d = 2. The wake profiles show that the velocity defect increases as increasing upstream cylinder’s diameter for L/d = 5.5. While this order cannot be accessed for L/d = 2. It is observed that sudden and unusual velocity defect happened for L/d = 2 and d/D = 0.8 cases, which means that the most velocity defect is running on. Also, numerical solution results of velocity profile have been compared with the mentioned experimental results at station 4 and velocity of 10 m/s for both L/d = 2 and 5.5. Results shows a little difference because of using one-dimensional Hot-wire.

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Study of a Real Fluid Flow Axial Symmetry in a Cylindrical Cavity

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.550-553.929 ◽

2012 ◽

Vol 550-553 ◽

pp. 929-933

Author(s):

A. Bouhenna ◽

Y. Salhi

Keyword(s):

Experimental Data ◽

Carbon Dioxide ◽

Cylindrical Cavity ◽

Theoretical Study ◽

Hot Wire ◽

Air Jet ◽

Real Fluid ◽

The Subject ◽

Flow Visualizations ◽

Solid Form

This paper is devoted to the experimental study of air jet in a cylindrical cavity initially containing air at rest. A set of experiments has been performed to analyze the velocity field in the cavity. The experimental data have been obtained by means of hot wire anemometry, in different sections of the cavity. In addition, flow visualizations were performed using carbon dioxide in solid form. Parallel to this work, we undertook a theoretical study on the same laminar flow, with the same geometric configuration, and it will be the subject to an incoming paper.

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Aeroelastic Dynamics of a NACA 0012 Airfoil in the Transitional Reynolds Number Regime

Volume 9: 6th FSI, AE and FIV and N Symposium ◽

10.1115/pvp2006-icpvt-11-93957 ◽

2006 ◽

Cited By ~ 5

Author(s):

Dominique Poirel ◽

Yael Harris ◽

Aze´mi Benaissa

Keyword(s):

Surface Roughness ◽

Reynolds Number ◽

Degrees Of Freedom ◽

Initial Conditions ◽

Reynolds Numbers ◽

Flow Structures ◽

Hot Wire ◽

Initial Work ◽

Naca 0012 ◽

The Relationship

The work discussed herein is a focused extension of a series of studies that were carried out at the Aeroelasticity Laboratory of the Royal Military College of Canada in recent years. Initial work revealed the presence of self-excited oscillations over certain ranges of airspeed when a NACA 0012 airfoil was immersed in the laboratory’s wind tunnel and allowed to oscillate freely in both pitch and heave. The range of airspeeds tested corresponded to Reynolds numbers in the low-to-moderate regime. While the aeroelastic apparatus is capable of two-degrees-of-freedom motion, the present work concerns only the motion of the airfoil when it is constrained to rotate in pure pitch. A parametric investigation is presently being undertaken to more fully comprehend the airfoil’s pitch behaviour, specifically the amplitude and frequency of its oscillations which are observed in the following range of chord based Reynolds numbers: 5.0 × 104 ≤ Rec ≤ 1.2 × 105. This paper focuses on the effect of the stiffness of the springs used in the apparatus. Other parameters such as surface roughness, turbulence intensity, temperature and initial conditions are also briefly discussed. In conjunction with the pitch oscillation measurements, preliminary results reveal vortices to be present in the wake. In an attempt to determine the frequency and character of these flow structures, as well as to understand the relationship between the airfoil motion and wake dynamics, hot-wire anemometry measurements have been performed.

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Turbulent transition in a truncated one-dimensional model for shear flow

Proceedings of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rspa.2011.0225 ◽

2011 ◽

Vol 467 (2135) ◽

pp. 3066-3087 ◽

Cited By ~ 4

Author(s):

J. H. P. Dawes ◽

W. J. Giles

Keyword(s):

Reynolds Number ◽

Shear Flow ◽

Turbulent Flows ◽

Temporal Dynamics ◽

Initial Conditions ◽

Initial Perturbation ◽

Initial Energy ◽

Chaotic Regime ◽

Transition To Turbulence ◽

Spanwise Direction

We present a reduced model for the transition to turbulence in shear flow that is simple enough to admit a thorough numerical investigation, while allowing spatio-temporal dynamics that are substantially more complex than those allowed in previous modal truncations. Our model allows a comparison of the dynamics resulting from initial perturbations that are localized in the spanwise direction with those resulting from sinusoidal perturbations. For spanwise-localized initial conditions, the subcritical transition to a ‘turbulent’ state (i) takes place more abruptly, with a boundary between laminar and turbulent flows that appears to be much less ‘structured’ and (ii) results in a spatio-temporally chaotic regime within which the lifetimes of spatio-temporally complicated transients are longer, and are even more sensitive to initial conditions. The minimum initial energy E 0 required for a spanwise-localized initial perturbation to excite a chaotic transient has a power-law scaling with the Reynolds number E 0 ∼ Re p with p ≈−4.3. The exponent p depends only weakly on the width of the localized perturbation and is lower than that commonly observed in previous low-dimensional models where typically p ≈−2. The distributions of lifetimes of chaotic transients at the fixed Reynolds number are found to be consistent with exponential distributions.

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